Thread: Testing to see if something is chnull in Unix

consider this definition:

Code:

#define chnull (char *)0
  
typedef struct 
  {
      int month,day,year;
  }DATE;
  
  typedef struct Key  KEY;
  typedef struct Key* KEYS;

  struct Key 
  {
      char *sender;
      char *addressee;
      char *regarding;
      DATE date;
      int id;
      char *fname;
      KEYS next;
  };

if I set any of the char strings to chnull...

Code:

...inside some function...
  //declare stuff 
  KEY temp;

  temp.fname=(char*)malloc(sizeof(20));
  temp.fname=chnull;

I cannot successfully test for a null value by doing

Code:

if( ! temp.fname )
nor by
if( temp.fname==chnull )

but I can test for a good value

Code:

if( temp.fname )

So in this case, what is the proper way to test that
temp.fname = chnull so that the test will evaluate to true?

Thanks in advance,
Mike

I can't change the define. This is a project where changing
the defines are not allowed.


I did make the change on the unix machine to test for chnull.
if ( temp.fname[0] == chnull )
the compiler complained. I got a warning:

bash-2.03$ cc -c -g search.c
cc: Warning: search.c, line 82: In this statement, "ki.fname[0]" of type "signed char", is being converted to "pointer to signed char". (cvtdifty
pes)
if(ki.fname[0]==chnull && ki.id==0)
---------------------------^
bash-2.03$

So I changed it to ki.fhame[0]==*chnull;
the compiler didn't complain, but I (still) crash when I execute the line
of code that contains that expression.

thanks